By Drs. David Niesel and Norbert Herzog
My mother used to say that I was going to give her grey hair, but what actually caused it was a reduction in the amount of a pigment called melanin. Scientists have now identified 18 genes that are associated with features and characteristics of hair including turning greying, thin eyebrows or a unibrow or why some men need to shave by early afternoon and why others cannot grow a beard at all. Hair is thought to serve many purposes including camouflage, thermal regulation, sensation and in social cues. Approximately 83 billion dollars is spent annually on hair care products globally, not to mention haircuts, wigs and other hair associated expenses, so obviously it is something we humans value.
Humans have lost the vast majority of their body hair but we have retained a substantial amount on our heads and it comes in a vast variety of colors, textures and types even before we start fooling with it. Natural hair color is an inherited trait. Variations in hair can be restricted by geography, for example, different hair colors are essentially restricted to Western Asia and Europe. Straight hair is all but absent in sub-Saharan Africa. Genes have been identified for baldness, hair colors and curliness. Two different genes have been found associated with straight hair, one in Europeans and another in East Asians suggesting that this trait arose independently at least two times.
The latest study involved a genome wide association study or GWAS in people of mixed European, Native American and African ancestry to identify genes associated with variations in hair. GWAS is a rapid method to scan genomes for genetic variations that are associated with diseases or other traits.
Natural hair color is determined by the amount of dark brown eumelanin and reddish pheomelanin. If a person makes a great deal of eumelanin, their hair will be black while a person with little will be blonde. Shades of red hair depend on the amount of pheomelanin compared to eumelanin. Genes for hair color include MC1R which determines how much pheomelanin is made. Now for the first time a gene for the graying of hair has been identified, IRF4, which turns on the TYR gene resulting in melanin production. One type of TYR gene leads to reduced melanin levels and lighter hair or the graying of hair. Stem cells in hair follicles renew the melanocytes that make melanin. These same proteins also appear to maintain melanocyte stem cells offering two possible mechanisms for going gray.
A gene called EDAR regulates the developmental location, size shape and density of hair follicles, particularly for beards. All told, 18 new genes associated with various features of hair were discovered. Most interventions to correct or change hair appearance rely on products that act on hair outside of the hair follicle. A furthering of our understanding of how and where hair grows could lead to the development of products that act on the hair as it grows. Could we block the graying of hair, change the shape, type and location of hair? Who knows, maybe we both could regain the hair we have lost over the years.
Medical Discovery News is hosted by professors Norbert Herzog at Quinnipiac University, and David Niesel of the University of Texas Medical Branch. Learn more at www.medicaldiscoverynews.com.